A plasma polymerization process for preparing proton-conducting electrolyte membranes from tetrafluoroethylene and water is presented. They can be deposited on different substrates, e.g., gas diffusion layers or as barrier layers on other polymer electrolyte membranes. An advantage of the plasma-polymerized membranes is their lower methanol permeability due to their highly cross-linked structure. Methanol permeation measurements with methanol solution exhibit methanol permeabilities which are by an order of a magnitude less than for Nafion® 115. The proton conductivity of the plasma-polymerized membranes varies from depending on deposition parameters.